Animal behaviors are governed by the endocrine and central nervous systems. An understanding of these processes requires and examination at the cellular and molecular level. The gastropod mollusc Aplysia is a particularly advantageous model system for studying questions of behavior due to its numerically simplified neural circuitry. These circuits have been correlated with a number of stereotyped behaviors. The physiological and behavioral aspects of egg laying in Aplysia are regulated by two tissues, the secretory atrial gland and the neuro-endocrine bag cells. Both release a battery of biologically active peptides. The action of atrial peptides cause the release of bag cell products which in turn elicit egg laying and the accompanying behavioral pattern. It is the goal of this project to understand this behavior in molecular detail. A multidimensional approach which draws on ideas and techniques from molecular, cellular and neurobiology will be used. The cloning of the neuropeptide genes has revealed a small gene family which gives rise to multiple transcripts and multiple polyproteins in each tissue. it is necessary to further investigate the organization of these genes and surrounding sequences. In particular we will study aspects of transcription in an attempt to understand the factors responsible for tissue specificity. It is also important to understand the processing of the polyproteins in the various cell types. In addition, peptide packaging into vesicles will be examined to see if multiple transmitters are co-released. The biological activities of the peptides defined from the sequences of recombinant DNA molecules will be investigated. Identified cells in the Aplysia nervous system provide a model system for determining postsynaptic effects of peptide transmitters. Eventually we would like to relate the activities of these neurons to behavior.